Eastbound traffic enters the Bay Bridge from the Essex and First Street onramps (lower right) in San Francisco, Calif. on Thursday, August 24, 2006. During the Labor Day weekend Caltrans will be closing the eastbound lanes approaching the Bay Bridge to demolish a 1,000 foot section of the upper deck (left).
PAUL CHINN/The Chronicle MANDATORY CREDIT FOR PHOTOGRAPHER AND S.F. CHRONICLE/ - MAGS OUT

Caltrans officials say they chose Labor Day weekend to close the lower deck of the Bay Bridge for construction because of the dearth of big events that tend to draw drivers into or out of San Francisco.

But they didn't consider the Sara Thierman-David Goldenberg wedding on Treasure Island. Or the sixth annual Art & Soul festival in downtown Oakland. Or dozens of other public and private events taking place on both sides of the bridge. Not to mention the people who like to take advantage of the three-day weekend to roam around the city.

"There's always something going on in San Francisco," said Bart Ney, a Caltrans spokesman. "But there weren't any really large events taking place over the weekend of the caliber that we see happening every single weekend through the end of the holidays."

For Thierman and Goldenberg, the Bay Bridge closure meant that the 150 of their 200 guests living or staying in San Francisco wouldn't be able to get to their Sunday wedding without circuitous drives over other bridges to Oakland then west on the Bay Bridge to the Treasure Island officers' club, a site they worked two years to secure.

"We thought we were going to have to move it," Thierman said. "We were even looking at getting ferries."

Instead, they hired charter buses to haul their guests between the wedding and the Transbay Terminal. The buses will only be allowed to run eastbound once an hour during the slot allowed for bus service.

"It's definitely not cheap," she said, "but in the scheme of things, it's not that bad. It's better than having to move the wedding."

Organizers of the sixth annual Art & Soul Oakland, a three-day music festival that takes place over 10 blocks in the city center, also feared the closure would deter some of the 75,000 to 80,000 expected attendees. But after working with Caltrans, BART and the Metropolitan Transportation Commission, organizers decided that the bridge closure might attract fans, given the event's location on several BART and AC Transit lines and proximity to the Oakland ferry terminal, said Sammee Roberts, executive producer of the festival.

Caltrans needs to close the lower deck to allow demolition crews to knock down and remove about 1,000 feet of the old upper level of the approach to the bridge from Beale Street west to the Clocktower lofts building. The work is part of a complicated project to remove the seismically unsafe double-deck approach built in the 1930s and replace it with stronger side-by-side structures without reducing the number of open lanes.

Labor Day weekend was chosen for the closure, Ney said, for three reasons:

-- The lack of big events, including festivals and professional sports games, in San Francisco.

-- Historic drops in traffic across the Bay Bridge compared with the following two weekends. Traffic counts from the past three years show the number of vehicles crossing the Bay Bridge to be about 7 percent lower on Saturdays, about even on Sundays and about 14 percent lower on Mondays.

-- The ability to complete the work in one three-day weekend instead of closing the bridge for two non-holiday weekends.

"That's the biggest reason," Ney said. "It allows us to do what would have taken two weekends in one long weekend."

Caltrans scheduled the closure for 11:59 p.m. Friday to allow 49er fans time to get across the bridge after the team's final exhibition game, expected to end about 10 p.m. To remind the 49er fans on Friday night, Caltrans is placing portable electronic signs in Monster Park parking lots and plans to run a video announcement on the giant scoreboard video screen.

Electronic highway signs as far south as San Jose and east to the Central Valley have warned drivers of the closure for more than a week. Message signs will also be posted at the McAfee Coliseum in Oakland, where the A's play Baltimore Saturday and Sunday and Texas on Monday. The visiting teams will make the trip from their San Francisco hotels on specially scheduled charter buses.

As part of the lower deck closure, eastbound on-ramps at First, Essex, Sterling, Fifth and Eighth streets will also be closed from 11:59 p.m. Friday until 5 a.m. Tuesday.

As soon as the traffic stops, crews from contractor Cleveland Wrecking will begin banging away at the upper deck, using 21 tractor-mounted hydraulic hammers trucked in from around the country. Sometime Saturday, they'll finish tearing up the deck and will begin knocking down support columns. Then they'll haul off the concrete and metal debris.

When the lower deck reopens Tuesday morning, the approach to the bridge will look a lot different to drivers, Ney said.

"It will be very noticeable," he said. "They will have sunshine for the first time in 70 years."

TRAFFIC

The bridge closes to eastbound traffic at 11:59 p.m. Friday -- about two hours after the 49ers' final exhibition game at Monster Park is expected to end. It won't reopen until 5 a.m. Tuesday.

BART

Longer trains will provide 24-hour service to a limited number of stations, stopping around 1 a.m. Tuesday, Sept. 5. Regular BART service resumes at 4 a.m. that day.

BUSES AND FERRIES

Limited cross-bay bus service will be provided hourly from the Transbay Terminal, and the Alameda/Oakland and Vallejo Baylink ferries will add extra boats and provide nearly hourly service.

ALTERNATE BRIDGES

Toll plazas are prepared for crowds.

RESOURCES

-- In late October or early November, eastbound Bay Bridge traffic will be detoured at about Fourth Street onto a temporary structure built beneath the westbound lanes and extending to Second Street. It will remain in use through 2007 while the current eastbound roadway is torn down and rebuilt.

-- The Harrison Street off-ramp, closed and demolished last year, will be rebuilt and reopen in early 2008.